Not applicable.
1. Field of the Invention
The present invention is directed generally to a planar optical display, and, more particularly, to a high contrast display panel and a method of making a high contrast display panel.
2. Description of the Background
Video display screens typically use cathode ray tubes (CRTs) for projecting an image onto the outlet face of the screen. A typical screen of this type has a width to height ratio of 4:3 with 525 vertical lines of resolution. An electron beam must be scanned both horizontally and vertically on the screen to form a number of pixels, which collectively form the image. Conventional cathode ray tubes have a practical limit in size and are relatively deep to accommodate the required electron gun. Larger screen televisions are available which typically include various forms of image projection for increasing the screen image size. However, such screens may experience limited viewing angle, limited resolution, decreased brightness, and decreased contrast, particularly in projection display screens.
It is known that optical panels can be created using a plurality of stacked waveguides, and an optical panel may be rendered black using at least one black cladding layer between transparent cores of the waveguides. The cladding layers have a lower index of refraction than the waveguide cores for effectuating total internal reflection of the image light channeled through the cores, and thereby improve contrast, i.e. thereby improve the appearance of black images on a screen.
In the typical television application using optical panels, the black areas are minimized in order to maximize the light transmission area, and to thereby improve screen brightness. However, the minimization of the black areas on the face of the optical panel does not allow for optimization of screen contrast, due to the fact that only increases in the black area allow for increases in screen contrast. Further, maximization of the light transmission area simultaneously increases the area that reflects ambient light, thereby further decreasing screen contrast and darkness.
Therefore, the need exists for a display panel that increases the appearance of the black area on the screen to thereby improve viewing contrast.
The present invention is directed to a high contrast optical panel. The optical panel includes a plurality of stacked optical waveguides, wherein each waveguide has an inlet face and an outlet face at opposing ends of each waveguide, and wherein each waveguide is formed of a core in contact with at least one cladding layer, wherein the at least one cladding layer includes at least one black layer, and at least one redirector connected to the inlet face of each of at least two waveguides. The at least one black layer has a first thickness, and the core has a second thickness, and the first thickness is preferably greater than the second thickness. In a preferred embodiment, the first thickness is at least two times greater than the second thickness. In a second preferred embodiment, the first thickness is at least four times greater than the second thickness.
The high contrast optical display panel solves problems experienced in the prior art by providing a display panel that increases the appearance of the black area on the screen to thereby improve viewing contrast. Further, the present invention reduces ambient light reflections from the light redirector.